Device for the pulsed release of an amount of fluid that is stored in a storage housing

ABSTRACT

A device for the pulsed release of an amount ( 3 ) of fluid that is stored in a storage housing ( 2 ), in particular for implementing a start-stop function in automatic transmissions, with a piston ( 5 ) that is supported against a first energy storage device ( 4 ) and that, with the capacity to move within the storage housing ( 2 ), limits in conjunction with the latter the amount ( 3 ) of fluid that can be held and that, when triggered by an actuation means ( 6 ) and released by a locking means ( 7 ), pushes the amount ( 3 ) of fluid out of the storage housing ( 2 ) in a pulsed manner, the locking means ( 7 ) having individual catch means ( 8 ) that in the locked position keep the piston ( 5 ) in its pretensioned position, and that, when actuated by the actuation means ( 6 ), release the piston ( 5 ) in a release position, is characterized in that in any travel position of the piston ( 5 ), the catch means ( 8 ) are at least partially in contact with the inside wall of the piston ( 5 ) facing them, and that for locking of the piston ( 5 ), the catch means ( 8 ) act in that end region ( 9 ) of the piston ( 5 ) that is located adjacent to the stored amount ( 3 ) of fluid.

The invention relates to a device for the pulsed release of an amount offluid that is stored in a storage housing, in particular forimplementing a start-stop function in automatic transmissions, with apiston that is supported against a first energy storage device and that,with a capacity to move within the storage housing, limits inconjunction with the storage housing the amount of fluid which can beheld and which, when triggered by an actuation means and released by alocking means, pushes the amount of fluid out of the storage housing ina pulsed manner, the locking means having individual catch means whichin the locked position keep the piston in its pretensioned position, andwhich, when actuated by the actuating means, release the piston in arelease position.

For reasons of saving fuel and minimizing pollutant emissions, insuitable operating states in modern motor vehicles, the internalcombustion engine is shut off. To enable driving despite of a so-calledengine start-stop function, a short starting process of the internalcombustion engine and an immediate closed linkage in the transmission ofthe vehicle is necessary.

In prior art automatic transmissions of vehicles or, for example, inautomatic gearboxes which are made with wet-running disk clutches, theclutches are adequately supplied with hydraulic fluid by way of a fluidsupply means only when the internal combustion engine is running. When aclosed linkage is established in this transmission, first the clutchplay must be overcome and the clutch or clutches must be completelyclosed by raising the fluid pressure. The equalization of the play ofthe clutch and its connection to the closed linkage are achieved byrouting an amount of fluid into the piston space of the hydraulicallytriggerable clutches which are to be connected, the amount of fluidbeing made available by the fluid supply means. When the vehicle startsoff again after the internal combustion engine had been shut off,potentially a plurality of switching elements in the transmission areopen and must be closed, as a result of which an unduly long timeinterval can transpire until a completely closed linkage in thetransmission is in fact established.

This disadvantage is resolved in prior art transmissions with ahydraulic pump that is driven by an electric motor and in which thedelivery volume of the pump is independent of the speed of the internalcombustion engine, and which, in the absence of pressure supply by wayof the main pump of the transmission in the hydraulic system, producesat least a pressure by means of which the clutch play can be equalized.The hydraulic pump which can be driven by the electric motor, however,leads to deterioration of the efficiency of the transmission and toincreased cost of the transmission. Moreover, not inconsiderableadditional installation space in motor vehicles and engineering effortare required for linking to the hydraulic system of the transmission andto an electrical control system.

DE 10 2006 014 756 A1 furthermore shows and describes a device forstorage and for the pulsed release of an amount of hydraulic fluid forthe transmission means of a motor vehicle, with a storage housing whichcan be dynamically connected to the transmission means for replacementof the amount of fluid and which is bordered by the storage space and amovable limiting means which is formed as a piston. The piston isarranged so that it can be displaced within the storage space and istriggered by an actuation means. The piston is furthermore held by alocking means in its pretensioned position. For this purpose, thelocking means has catch means which keep the piston in a pretensionedposition in its against a first energy storage device which is formed asa compression spring. The locking means can be moved by the actuationmeans into a release position for the piston, the amount of fluid inthis case being delivered pulsed into the transmission means which ismade, in particular, as an automatic transmission.

With such devices, essentially, amounts of fluid matched to the demandof a specific consumer can be set in a defined manner for obtaining apractical engine start-stop function for automatic transmissions. Theprior art devices have at least a complex structure or require notinconsiderable installation space which, as a rule, only rarely isavailable in vehicles in the desired scope.

Furthermore, the locking means and the actuation means of these devicesare generally often unnecessarily complex since the number of theirparts is not exactly minimized with reference to representing thenecessary functions.

Proceeding from this prior art, the object of the invention is to devisea device, the pulsed release of an amount of fluid that is stored in astorage housing, in particular for implementation of a start-stopfunction in automatic transmissions which is not only reliable and whichrequires little installation space, but which can be easily produced andis especially durable and wear-resistant and, in particular, can ensurecontinuous operation, as this constitutes the start-stop function inautomatic transmissions.

This object is achieved with a device with the features of claim 1 inits entirety.

In that, as specified in the characterizing part of claim 1, in anytravel position of the piston the catch means are at least partially incontact with the inside of the piston facing them, and, in that, forlocking of the piston, the catch means act in that end region of thepiston that is located adjacent to the stored amount of fluid, anadditional component or several components for prepositioning of thecatch means and for ensuring reliable engagement of the catch means withthe catch surfaces for purposes of locking of the piston in a positionin which the maximum of the amount of fluid is stored in the storagehousing is not necessary. The piston of the device, due to itsconfiguration according to the invention, undertakes prepositioning ofthe catch means for purposes of their later locking.

The catch means are held by the locking means in this position relativeto their storage housing, that in the piston position in the storagehousing, which corresponds to the maximum of the storable andretrievable amount of fluid, the catch means engage that end region ofthe piston which is adjacent to the stored amount of fluid. The catchmeans accordingly act in the pretensioned position of the piston in thevicinity of the back of the piston bottom. This configuration of thepiston according to the invention thus effects an absolute maximum ofthe storable amount of fluid using the maximum possible travel path ofthe piston, associated with a minimum of required installation space andtotal number of parts of the device.

With the device according to the invention it is possible to makeavailable an amount of fluid which is defined by the size of the storagespace for supply of at least one consumer of an automatic transmission,and to feed it pulsed into the automatic transmission such that a timeinterval transpires which is not noticeable to the driver of the vehicleuntil transmission shifting functions or clutch functions are availableafter starting of the internal combustion engine of the vehicle. Thedevice has a very reliable structure so that immediate readiness fordriving after the internal combustion engine of the vehicle has beenstopped is always possible over a long service life of the internalcombustion engine.

In one preferred embodiment of the device there is a holding means forthe catch means which is part of the locking means and is preferablyfixed on the storage housing. The holding means additionally assumes thefunction of guiding or positioning the actuation means. Preferably theholding means is structured such that it guides at least components ofthe actuation means or that the actuation means which triggers the catchmeans is made to be displaceable relative to the holding means. Thedevice according to the invention for the pulsed release of an amount offluid stored in the storage housing is thus characterized by multipleuse of individual components relative to different functions combined inone component; this is advantageously reflected in the minimization ofthe number of parts and thus the production costs and installationcosts. Moreover, problems in operation of the device according to theinvention are virtually precluded due to the reduced number of parts.

As the aforementioned illustrates, especially in the configuration ofthe piston is improved operation of the device substantiated. Thus, inthe end region of the piston along its inner wall side, preferably inthe vicinity of the bottom of the piston, there are catch surfaces whichcan be moved into locked engagement with the catch means and which hold,upon locking in the piston, against the action of the first energystorage device. The piston assumes a position which corresponds to amaximum of the amount of fluid to be stored in the storage housing. Thecatch means and the catch surfaces, likewise in its entirety as thelocking means as a whole with the actuation means, are madewear-resistant such that they withstand the number of working cycleswhich corresponds at least to the service life of that component of thehydraulic system, particularly an automatic transmission, with which thedevice interacts.

If locking of the piston on the holding means of the catch means iscancelled, the piston is moved pulsed with relief of the first energystorage device into a position in the storage housing which correspondsto the minimum of the stored amount of fluid. In the process, the catchmeans are moved into the locked position by the actuation means which ispreferably guided on the holding means. The amount of fluid located inthe storage housing is promptly expelled and is immediately available toa hydraulic consumer according to the demand for a starting function forthe internal combustion engine of the vehicle.

The hydraulic consumer is thus virtually at the same time with theinternal combustion engine in a ready-to-operate situation and ispreferably able to implement shifting processes and the like in theautomatic transmission. This enables operation of the vehicle with astart-stop function without a significant adverse effect on the driver.

Essentially, the actuation means can form a hydraulically orpneumatically operating system or a mechanical system. In one especiallypreferred embodiment, there is preferably a magnet system, preferably anelectromagnet system, which is used for actuating the actuation plunger.The actuation plunger can be moved both as an armature by anelectromagnetic coil into one or more positions and can be kept therein.But it is advantageous to provide a second energy storage device whichkeeps the actuation plunger in the initial state in the unactuated,preferably de-energized state of the electromagnetic coil. This initialstate of the actuation plunger is preferably defined by the catch meansbeing engaged to the end region of the piston.

The catch surfaces, which interact with the catch means on the holdingmeans for purposes of locking of the piston, are located on the endregion of the inner periphery of the piston. They are formed in oneespecially preferred embodiment at the transition between thecylindrical guide surface on the inner periphery of the piston toward acatch chamber which widens in diameter. Preferably, for the catchsurfaces there are oblique surfaces on which the catch means can bemoved from an unlocked position into a locked position and vice versa bysliding or rolling off. By choosing the angle of the oblique surfacesrelative to the other cylindrical guide surfaces, quiet, reproduciblelocking can be achieved without any hindrance by clamping or inhibitionof the catch means. Moreover, this design measure enables virtuallywear-free operation of the device over the long term.

In one especially advantageous embodiment, the holding means is made asa hollow cylinder which is located stationary relative to the storagehousing and is preferably directly and securely connected to it.

The holding means for the catch means advantageously takes over guidanceof at least one actuation plunger of the actuation means. Othercomponents of the actuation means which are not explicitly named can beguided on the holding means.

It is advantageous, especially when the holding means is made as ahollow cylinder or as a bolt-like or pin-like element which extends inthe direction of motion of the piston, to form on the outer periphery ofthe holding means a stop which comes into contact with one free end ofthe piston when the piston is in the position which corresponds to themaximum of the volume of the amount of fluid in the storage housing. Thepiston can be supported on the stop in this position which it assumesfor a pretensioned, first energy storage device. That way, the piston isalways fixed in its two end positions in the storage housing such that,for example, vibrations, which are transferred to the device byoperation of the internal combustion engine, do not generate any furtheroperating noise of the device. Moreover, this ensures that areproducibly exact storage volume of the amount of fluid can always bemade available by the device.

The catch means are preferably made as rolling elements, especially ascatch balls. In particular, the standardized surface hardnesses of therolling elements have a positive effect on serial production and theconstruction of the device. The rolling elements or catch balls can beeasily accommodated in cage-like recesses in the holding and/or lockingmeans. It can be feasible, in a modified embodiment, instead of rollingelements to use, for example, rocker-like catch cams which are guided ontheir one free end in a receiver of the holding means and which aresupported with their other free end with the capacity to be triggered bythe actuation means. With catch cams that are produced specifically intheir shape for the respective application, optimized, cam drive-likeinteraction of the catch means with the actuation means and the pistoncan be effected, as a result of which the expulsion motion of the pistonand thus the response speed of the device potentially are still furtherimproved. In particular, in this way, smooth response behavior for theinterlocking means is ensured.

Reliable operation of the device is further supported in that the firstenergy storage device is guided along the outer periphery of the pistonby the piston and the holding means and that the second energy storagedevice is guided in the holding means, in particular in the hollowcylinder, and in doing so encompasses the actuation plunger. The energystorage devices are preferably made as compression springs andparticularly as cylindrical helical compression springs. Their turns canhave a uniform spring constant or one which varies with the length ofthe springs in order to obtain optimized filling processes depending onthe shape and type of the hydraulic consumer to be filled and in orderto suppress the formation of gas bubbles, for example, in the consumers;this otherwise can lead to damaging cavitation effects in the hydrauliccircuit.

The invention is detailed below using embodiments shown in the drawings.The figures are schematic and not to scale.

FIG. 1 shows a longitudinal section through a device for the pulsedrelease of an amount of fluid that is stored in a storage housing in thefluid-filled state;

FIG. 2 shows a longitudinal section through the device as shown in FIG.1 in the emptied state;

FIG. 3 shows a longitudinal section through another device for thepulsed release of an amount of fluid that is stored in a storagehousing; and

FIG. 4 shows a longitudinal section through the device as shown in FIG.3 in the emptied state.

FIG. 1 shows, in a longitudinal section, a device 1 for the pulsedrelease of an amount 3 of fluid that is stored in a storage housing 2.The device 1 is used to store a working agent for consumers of ahydraulic system (not detailed) which is used, for example, for storageand pulsed release of hydraulic fluid for the shifting cylinder of theautomatic transmission of an automobile. Other applications areconceivable where it is crucial to have a specific amount of fluid madeavailable in a pulsed manner.

The cylindrical storage housing 2 has a first energy storage device 4which is made as a cylindrical compression spring. The energy storagedevice 4 is used to apply a definable compressive force to a piston 5,which force is sufficient to move, in a pulsed manner, the piston 5 outof a locked position, shown in FIG. 1, into a position in which theamount of fluid 3 is expelled from the storage housing 2 (compare FIG.2). The amount of fluid 3 in the position of the piston 5 that is shownin FIG. 1 is delivered pressurized into the storage housing 2 by aconventional fluid conveying means, such as, for example, a rotary pump.The piston 5 is kept in the illustrated pretensioned position as shownin FIG. 1 by a locking means 7 that holds the piston 5 with catch means8 after the filling process.

In order to achieve pulsed expulsion of the amount 3 of fluid from thestorage housing 2, there is an actuation means 6 with which the catchmeans 8 can be moved into a position in which the locking on the endregion 9 of the piston 5 is released. The end region 9 of the piston 5which the catch means 8 engage in the locked position of the piston 5 islocated opposite the stored amount 3 of fluid, as a result of which themaximum travel path of the piston 5 in the storage housing 2 is enabled.

The catch means 8 in the embodiments shown in FIGS. 1 to 4 are kept in aposition that cannot be axially changed on the holding means 11 that ismade as a hollow cylinder 21. For temporary locking of the catch means 8to the piston 5 and for reliably assuming a releasable, pretensionedposition of the piston 5, the piston 5, along its inner side 12, hascatch surface 13 that can be moved into locking engagement with thecatch means 8 (compare FIG. 1).

The actuation means 6 shown in FIGS. 1 to 4 are formed essentially froma multi-part, stepped, cylinder-like actuation plunger 15, which,axially guided by a magnet system 14, can be axially moved in theholding means 11. FIG. 2 depicts the actuation plunger 15 in an initialstate in which it is held by a second energy storage device 16 formed asa helical compression spring, the catch means 8 disengaging from the endregion 9 of the piston 5 and the second energy storage device 16 havinga maximum length.

In the embodiments of the device 1 which are shown in FIGS. 1 to 4, thecatch surfaces 13 are located along the cylindrical inner periphery 17of the end region 9 of the piston 5 and are formed, in particular, by alinear transition 18 between the cylindrical guide surfaces 19 of thepiston 5 and a catch chamber 20 which widens in diameter. Accordingly,the inner periphery 17 and the indicated inner side 12 form parts of theinner wall of the piston 5 facing the catch means 8. The catch chamber20 is in turn axially bordered by the bottom of the piston 5 so thatoverall a maximum possible travel path of the piston 5 is achievedbefore locking takes place here. The piston 5 in the locked positionshown in FIG. 1, with its free end facing away from the amount 3 offluid, adjoins a stop 22 on the outer periphery of the holding means 11and, in this way, is held axially unable to move between the catch means8 and the stop 22.

FIGS. 1 and 2 show examples in which the catch means 8 are made asrolling elements 23, in particular catch balls 24, which in their axialposition are held by cage-like recesses 25 in the end region of theholding means 11. The catch balls 24 are supported either radially onthe catch surface 13 which are formed as a roughly 45 degree obliquesurface oriented away from the holding means 11, on the end region 9 ofthe piston 5 which forms the catch chamber 20 (compare FIG. 1), or thecatch balls 24 are supported on the inner side 9 of the piston 5 on thecylindrical guide surfaces 19 of the piston 5 itself. Viewed radially inthe direction to the actuation plunger 15, the catch balls 24 aresupported on a cylindrical thickened control part 30 of the actuationplunger 15. The control part 30 has a peripheral groove 31 whose flanksform catch surfaces or oblique surfaces for changing the radial positionof the catch balls 24. The oblique surfaces or flanks of the peripheralgroove 31 in the control part 30 are shaped such that in a relativetravelling motion of the control part 30 to the cage-like recesses 25 inthe holding means 11, the catch balls 24 are pressed radially to theoutside, but remain in the recesses 25 as soon as the catch surfaces 13in the catch chamber 20 of the piston 5 reach the vicinity of the recess25 or are congruent to the cage-like recesses 25.

In the embodiments shown in FIGS. 1 to 4, the holding means 11 is madeas a cylinder which has an outside diameter which is roughly half thatof the storage housing 2. The piston 5 on its side facing away from thefluid amount 3 is shaped as a cylindrical sleeve 32, the sleeve 32 beingconnected in one piece to the piston 5. The sleeve 32 slides on theouter periphery of the holding means 11. For the sake of simplerrepresentation, the holding means 11 is shown as made in one piece withthe cover 33 that closes off the storage housing 2 toward the magnetsystem 14. The wall 34 of the storage housing 3 is flanged with thecover 33, a radial peripheral bead 34 oriented toward the wall 34 on thecover 33 being fitted into the wall 34 and thus forming an additionalpositive connection between the cover 33 and the wall 34.

Furthermore, the cover 33 has a cylindrical receiver 36 for centeringthe electromagnet 37 of the magnet system 17, which electromagnet isflanged to the cover 33. The actuation plunger 15 is connected by way ofa set screw 38 to the armature of the magnet system 14 which is notdetailed so that precision calibration of the position of the actuationplunger 15 relative to the holding means 11 can take place. The setscrew 38 is fixed by a lock nut 39 in contact with the actuation plunger15.

FIG. 1 shows the electromagnet 37 in the de-energized state and thesecond energy storage device 16 assumes its extended position in whichit pulls the control part 30 to an axial stop on the inner periphery ofthe holding means 11. The stop 40 is located on the free end 10 of theholding means 11. The second energy storage device 16 which is madelikewise as a cylindrical compression spring is located in a cylindricalspring space 41 between the actuation plunger 15 and the holding means11 and is supported on point 42 of the actuation plunger 15 and on theannular stop 43 of the holding means 11. If the actuation plunger 15,viewed from overhead in FIG. 1, is pushed to the right by the magnetsystem 14, the control part 30 is pushed in the same way to the rightand the catch balls 24 can reach the peripheral groove 31 in the controlpart 30 of the actuation plunger 15. This takes place under the actionof transverse forces F_(Q) (compare FIG. 2) which act continuously inthe locked state of the piston 5 from its oblique catch surfaces 13radially in the direction to the longitudinal axis 44 of the storagehousing 2.

The piston 5 is released and moved in a pulsed manner to the right asfar as its contact with a second cover 45 of the storage housing 2 underthe action of the compressive force of the first energy storage device4. The first energy storage device 16 is supported on the cover 33 andon the back of the piston 5 that is facing away from the fluid amount 3.The entire fluid amount 3 stored in the storage housing 2 is promptlyexpelled from the storage housing 2 and is supplied to a consumer in amanner which is not detailed (compare FIG. 2).

In all the illustrated embodiments there is a sealing element 46 in theform of a piston ring in the peripheral groove of the piston 5. Thesecond cover 45 bears a flat flange 47 which is oriented in thedirection of the longitudinal axis 44 for attachment of the device 1.Furthermore, the cover 45 with its thick-walled bottom forms a receiverfor a screw-in valve 48 which is not detailed and which can comprise anonreturn valve and a pressure limiting valve or flow control valve. Thecover 45 screwed on the storage housing 2 can be attached with theinterposition of a sealing element 49, as is illustrated in FIGS. 1 to4.

FIGS. 3 and 4 each show a longitudinal section through a device 1 ofessentially similar structure, the pulsed release of an amount 3 offluid that is stored in a storage housing 2, which, however, differsfrom the embodiment as shown in FIGS. 1 and 2 in the structure of theholding means 11, the locking means 7 and the actuation means.

The actuation plunger 15 over its length has an almost uniform outsidediameter and is formed in one piece with its end-side control part 30. Aperipheral groove 31 in the control part 30 has a greater width than inthe embodiment as shown in FIGS. 1 and 2. The catch means 18 are shapedas catch cams 26 made in the form of rockers and have a rail-likeprofile in the longitudinal section. The catch cams 26 have a first freeend 27 with which they are held to be able to pivot into a receiver 28which is formed as a radially outer peripheral groove on the end 10 ofthe holding means 11. With its respective other free end 29, the catchcams, of which only two of a plurality are shown, are guided to engagethe peripheral groove 31 in the control part 30. The catch projections50 of the catch cams 26, which projections engage the receiver 28 andthe peripheral groove 31, are made asymmetrical and have smaller catchprojections 51 which are directed radially to the outside, with whichthe catch cams 26 can slide along the inner side 12 of the piston 5.FIG. 3 shows the position of the piston 5 which corresponds to themaximum amount 3 of fluid in the storage housing 2, the actuationplunger 15 by expansion of the second energy storage device 16 causingin a assumes a position moved to the magnet system 14.

By this travelling motion of the actuation plunger 15, the catchprojection 50 that faces the piston 5 is displaced out of its position(compare FIG. 4) which lies in the peripheral groove 31 and movesradially to the outside onto the catch surfaces 13 which are likewisemade as oblique surfaces in the catch chamber 20. This results in thepiston 5 being locked. In FIG. 4 the actuation plunger 15 is moved tothe right by the electromagnet 37, viewed from overhead in FIG. 4, as aresult of which the catch projection 50 can drop into the peripheralgroove 31 in the control part 30 of the actuation plunger 50 and indoing so releases the piston 5. The piston 5 is thus able to release theamount 3 of fluid in a pulsed manner under the action of the firstenergy storage device 4.

1. A device for the pulsed release of an amount (3) of fluid that isstored in a storage housing (2), in particular for implementing astart-stop function in automatic transmissions, with a piston (5) thatis supported against a first energy storage device (4) and that, withthe capacity to move within the storage housing (2), limits inconjunction with the latter the amount (3) of fluid which can be heldand that, when triggered by an actuation means (6) and released by alocking means (7), pushes the amount (3) of fluid out of the storagehousing (2) in a pulsed manner, the locking means (7) having individualcatch means (8) that in the locked position keep the piston (5) in itspretensioned position, and that, when actuated by the actuation means(6), release the piston (5) in a release position, characterized in thatin any travel position of the piston (5), the catch means (8) are atleast partially in contact with the inside wall of the piston (5) facingthem, and that, for locking of the piston (5), the catch means (8) actin that end region (9) of the piston-(5) that is located adjacent to thestored amount (3) of fluid.
 2. The device according to claim 1,characterized in that the catch means (8) of the locking means (7) areheld on the free end (10) of a holding means and the actuation means (6)that can be triggered the catch means (8) is held able to move relativeto the holding means (11).
 3. The device according to claim 1,characterized in that in the end region (9) of the piston (5) along itsinner side (12) as part of the inner wall, there are catch surfaces (13)which can be caused to engage the catch means (8) by locking and inlocked engagement of the piston (5) pushed against the action of thefirst energy storage device (4), a maximum of the amount (3) of fluid tobe stored is accommodated by the storage housing (2).
 4. The deviceaccording to claim 3, characterized in that with release of the catchmeans (8) by the actuation means (6), the piston (5), under the actionof the first energy storage device (4), expels the stored amount (3) offluid from the storage housing (2) in a pulsed manner.
 5. The deviceaccording to claim 1, characterized in that the actuation means (6)holds an actuation plunger (15) that can be actuated by means of amagnet system (14) and that, under the action of a second energy storagedevice (16), without the magnet system (14) actuated, is held in theinitial state in which the catch means (8) engage the end region (9) ofthe piston (5).
 6. The device according to claim 1, characterized inthat the catch surfaces (13), which are located along the innerperiphery (17) of the end region (9) of the piston (5), are formed by atransition (18) between the cylindrical guide surface (19) for therespective catch means (8) and a catch chamber (20) which widens indiameter relative to the guide surface (19).
 7. The device according toclaim 1, characterized in that the holding means (11) forms a hollowcylinder (21) which is securely connected fixed to the storage housing(2) and that the actuation means (6) with its actuation plunger (15) isguided in the hollow cylinder (21).
 8. The device according to claim 3,characterized in that the holding means (11) along its outer peripheryforms a stop (20) for contact of the free end (9) of the piston (5),which end faces the stop (22), which is supported on the stop (22) withthe first energy storage device (4) pretensioned at a maximum of theamount (3) of fluid held in the storage housing (2).
 9. The deviceaccording to claim 1, characterized in that the respective catch means(8) consist of rolling elements (23) such as catch balls (24) that areheld in cage-like recesses (25) in the holding means (11).
 10. Thedevice according to claim 1, characterized in that the respective catchmeans (8) consist of rocker-like catch cams (26) that on their one freeend (27) are guided in a receiver (28) of the holding means (11) and canbe triggered on their other free end (29) by the actuation means (6).11. The device according to claim 2, characterized in that the firstenergy storage device (4) is guided along the outer periphery of thepiston (5) by the piston (5) and the holding means (11) and that thesecond energy storage device (16) guided in the holding means (11)encompasses the actuation plunger (15).